Cubic　Sb　2O　3　nanocrystalline　was　obtained　via　a　precipitation　method.　The　sample　was　characterized　by　X-ray　diffraction　(XRD)　analysis,　scanning　electron　microscopy　(SEM),　transmission　electron　microscopy　(TEM),　UV-Vis　diffuse　reflectance　spectroscopy　(DRS)　and　electron　spin　resonance　(ESR),　etc.　The　photocatalytic　degradation　of　methyl　orange　under　UV　irradiation　as　a　model　reaction　was　used　to　evaluate　the　photocatalytic　properties　of　the　material.　The　results　revealed　that　Sb　2O　3　nanocrystalline　prepared　by　the　precipitation　method　exhibited　small　particle　size　and　high　photocatalytic　activity.　Factors　affecting　the　photocatalytic　activity　of　the　as-prepared　Sb　2O　3　nanocrystalline　are　discussed,　and　a　possible　mechanism　of　the　photocatalytic　degradation　of　methyl　orange　over　the　cubic　Sb　2O　3　nanocrystalline　is　also　proposed.